This invention relates to hydraulic power steering systems for vehicles, such as cotton harvesters, of the type having a pair of front driving wheels and a rear steerable guide wheel assembly pivotally mounted to the vehicle frame on a vertical axis, and more particularly, to a simple, economical apparatus for obtaining direct hydraulic control of the steerable wheel assembly.
Vehicles of the type described above have previously been provided with a hydrostatic power steering system wherein a manual gerotor pump is connected directly to the steering wheel in the operator's compartment and hydraulically connected to a frame-mounted reciprocating hydraulic servo-motor comprising a cylinder closed at both ends and having a double-ended piston slidable therein, the piston being provided with a rack type gear which meshes with a pinion gear mounted on the vertical pivot shaft of the steerable guide wheel assembly. One of the desirable characteristics of this system is that even though there is no mechanical linkage between the operator's steering wheel and the steerable guide wheel assembly, the same angular movement of the steering wheel will cause the same proportionate angular movement of the steerable guide wheel assembly in either the left or the right direction. This is because the gerotor pump provides the same output in either direction of rotation thereof and because both ends of the servo-motor cylinder have the same area. While this steering system operates very satisfactorily, the servo-motor and its rack and pinion gearing with the guide wheel assembly pivot shaft are an expensive way of achieving control of the steerable guide wheel assembly.
Accordingly, it is the primary object of the invention described and claimed herein to provide a vehicle of the type described above with a simple apparatus for directly controlling the steerable guide wheel assembly with a hydraulic cylinder while maintaining the same proportional angular relationship between the steering wheel and the steerable guide wheel assembly in either direction.
A more specific object of the invention is to interconnect the vehicle frame and the guide wheel pivot shaft with a control apparatus including a double-rodded, double-acting hydraulic cylinder.
Another specific object of the invention is to provide a means of introducing the hydraulic fluid to the cylinder body in such a manner as to minimize the required amount of movement of the hydraulic hoses supplying fluid to the hydraulic cylinder.
The above objects are specifically met in a steering system for a vehicle having a main frame structure including a transverse beam and a steerable rear guide wheel assembly pivoted on a transversely central vertical axis thereto, the steering apparatus including an actuating arm rotatably coupled with the guide wheel assembly, a double-rodded, double-acting hydraulic cylinder having its cylindrical housing pivotally mounted on the actuating arm and one of the ends of the cylinder rod pivotally mounted to the vehicle frame, and hydraulic means associated with an operator controlled steering wheel for controlling and delivering fluid to the cylinder. The hydraulic cylinder rod is preferably drilled axially from both ends to points just short of the piston thereon and a passage communicates from the axial holes respectively to each of the cylinder chambers. The hydraulic hoses connect to the rod adjacent the pivotal mounting of the rod to the frame and at the free end of the rod.